The present invention relates to pattern recognition systems, and more particularity to the pattern recognition systems that are used in-conjunction with the wire bonding machine for bonding opposite ends of wires to a semiconductor chip and lead frame.
Conventionally, wire bonding machines are widely used for connecting a semiconductor chip to a lead frame by bonding opposite ends of a plurality of wires such as gold wires to a semiconductor integrated circuit chip and innerleads of a lead frame, respectively for manufacturing a semiconductor package. These wires are used as input connections to the integrated circuit chips. The lead frame often are sufficiently robust to be inserted into a printed circuit board and soldered to conductors on the board.
These semiconductor packages are used with miniature electronic circuits or micro circuits which are used in vast quantities in a wide variety of consumer, commercial, industrial and military apparatus. The majority of such micro-circuits are of the type referred to as integrated circuits. These integrated circuits include a large number of active circuit elements such as transistors and passive elements such as resistors and capacitors. In semiconductor integrated circuits, conductive paths between circuit elements on a semiconductor substrate are formed by selectively etching the substrate. In hybrid micro-circuit circuit elements mounted on a ceramic substrate are usually interconnected, typically by conductive ink paths on the substrate.
The functional portions of integrated circuits are typically in the form of very small, rectangular-shaped chips, ranging in size from 0.025 inch to 0.200 inch or more on a side.
Conventional semiconductor wire bonders use X-Y tables to move the bond head over the semiconductor devise for bonding lead wires between the by semiconductor device, to its lead frame fingers. Sometimes, the lead frame is replaced by other appropriate electrical connections such as a ceramic package, hybrid circuit or other semiconductor device. The X-Y coordinate tables are driven by complex mechanical components that convert the rotatory motion of the axis drive motor to control linear motion. The bond head carries several components such as a Z-axis drive motor, a camera for vision functions and other components required to bond the lead wires. A camera or vision apparatus may be mounted at the pivot point of the bond head frame and views the bonding area through lenses and 45xc2x0 mirror prisms.
The lead frame is moved or xe2x80x9cindexxe2x80x9d to a location where an accurately cut piece of thermoset film is attached precisely to the bottom side of the lead frame.
This camera or pattern recognition apparatus are widely used in modem manufacturing processes to position work items with precision. In the manufacture of hybrid integrated circuits, for example, such equipment is frequently incorporated in the automatic wire bonding machines. Components must be positioned within an acceptable precision before bonding takes place less connections be mislocated and produces results which either require repair or must be discarded.
The pattern recognition apparatus may include a television camera for creating an image of the work item and a processor for converting the image of the work item to digital form. The processor uses selected threshold values to determine which gray value is to be digitized as black instead of white. The picture or image elements (referred to in the art as pixels) of the digitized imaged are compared with those of a digitized reference image of the work items stored in memory. The pattern recognition apparatus then not only generates off set coordinates, giving the apparent location of a work item image with reference to a base location, but also generates a quality number representing the extent of match between pixels of the digitized work item image and those of the digitized reference image. If the quality number is at least as large as a predetermined quality reference level the offset coordinates are accepted as correct and used to control servo mechanism which positions the work item.
FIG. 1 illustrates a matrix lead frame 100 with two missing dies. The wire bonding machine operates according to the algorithm illustrated in FIG. 2. At die position 101 alignment with the die is attempted and a successful bond is achieved The bonding machine moves to die position 103. Alignment is achieved with the die, with the wires being bonded, and the bonding machine moves to die 105. Again alignment is achieved, and the wires are bonded to die 105. The bonding machines moves to die position 107. At die position 107, the bonding machine is aligned at die position 107, and wires are bonded at die position 107. Next, the bonding machine moves to die position 109. However, when alignment is attempted at the position, the alignment can not be made and the bonding machine stops for manual assistance. When the machine stops for manual assistance, labor costs increase, machine utilization of the bonding machine, decreases and yield of bonded dies decreases. However, in a great many cases, the problem with the alignment is not the fact that a die is actually missing, but the problem is that the bonding machine confuses the absence of the die with either a combination of die and epoxy or a combination of die and die pad.
The present invention provides a bonding machine with a pattern recognition apparatus that can discriminate between a die, and epoxy or a die pad or any of the combinations. By more accurately determining whether or not a die is present, increased manpower can be realized, the utilization of the bonding machine can be increased and the yield of semiconductor bonded to lead frames can be sufficiently increased. The present invention converts pixel data to discrimination data that can be employed to discriminate between die, die pad or epoxy The present invention converts the pixel data to gray level data and gray level variation data in order to obtain the discrimination data. The present invention by utilization of gray level and gray level variation in combination with several test algorithms determines the discrimination data in order to obtain a high degree of accuracy of whether a die, epoxy or die pad or any of the combination of the above are present.